Fatigue behavior of aluminum and copper metallization for SiC during APC

A copper based-top side metallization for silicon carbide semiconductors (SiC) is tested in active power cycling to enhance the reliability. In the tested samples failure is shifted to the die attach of the chip compared to the reference samples with Al metallization. This paper focuses on two degradation mechanism at the top-side-assembly and interconnection technology (AIT). The degradation of the free metallization surface, caused by thermomechanical stress, is evaluated in simplified bending tests. This mechanism involves the formation of extrusion and intrusion. The second mechanism involves vertical crack growth in the copper metallization, starting next to the bond. This crack is observed in active power cycling (APC) tests and in bending tests of a substrate with metallization layer and bond. Cross-sections of several tested samples are analysed to understand the crack growth behaviour after different cycles and under various loading conditions. The simplified bending tests as well as in the APC tests demonstrate that the crack can reach the cell field of the chip. Furthermore, the simplified bending test demonstrate that the critical strain amplitude required for crack growth is like the optically determined critical load for surface degradation at high cycle counts.